<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<link rel="STYLESHEET" href="lib.css" type='text/css' />
<link rel="SHORTCUT ICON" href="../icons/pyfav.png" type="image/png" />
<link rel='start' href='../index.html' title='Python documentation Index' />
<link rel="first" href="lib.html" title='Python library Reference' />
<link rel='contents' href='contents.html' title="Contents" />
<link rel='index' href='genindex.html' title='Index' />
<link rel='last' href='about.html' title='About this document...' />
<link rel='help' href='about.html' title='About this document...' />
<link rel="next" href="optparse-callback-example-4.html" />
<link rel="prev" href="optparse-callback-example-2.html" />
<link rel="parent" href="optparse-option-callbacks.html" />
<link rel="next" href="optparse-callback-example-4.html" />
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<meta name='aesop' content='information' />
<title>14.3.4.6 Callback example 3: check option order (generalized)</title>
</head>
<body>
<div class="navigation">
<div id='top-navigation-panel' xml:id='top-navigation-panel'>
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="14.3.4.5 callback example 2:"
  href="optparse-callback-example-2.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></a></td>
<td class='online-navigation'><a rel="parent" title="14.3.4 option Callbacks"
  href="optparse-option-callbacks.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up one Level' width='32' /></a></td>
<td class='online-navigation'><a rel="next" title="14.3.4.7 callback example 4:"
  href="optparse-callback-example-4.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></a></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></a></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></a></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="optparse-callback-example-2.html">14.3.4.5 Callback example 2:</a>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="optparse-option-callbacks.html">14.3.4 Option Callbacks</a>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="optparse-callback-example-4.html">14.3.4.7 Callback example 4:</a>
</div>
<hr /></div>
</div>
<!--End of Navigation Panel-->

<h3><a name="SECTION0016346000000000000000"></a><a name="optparse-callback-example-3"></a>
<br>
14.3.4.6 Callback example 3: check option order (generalized)
</h3>

<p>
If you want to re-use this callback for several similar options (set a
flag, but blow up if <code>"-b"</code> has already been seen), it needs a bit of
work: the error message and the flag that it sets must be
generalized.
<div class="verbatim"><pre>
def check_order(option, opt_str, value, parser):
    if parser.values.b:
        raise OptionValueError("can't use %s after -b" % opt_str)
    setattr(parser.values, option.dest, 1)
[...]
parser.add_option("-a", action="callback", callback=check_order, dest='a')
parser.add_option("-b", action="store_true", dest="b")
parser.add_option("-c", action="callback", callback=check_order, dest='c')
</pre></div>

<p>

<div class="navigation">
<div class='online-navigation'>
<p></p><hr />
<table align="center" width="100%" cellpadding="0" cellspacing="2">
<tr>
<td class='online-navigation'><a rel="prev" title="14.3.4.5 callback example 2:"
  href="optparse-callback-example-2.html"><img src='../icons/previous.png'
  border='0' height='32'  alt='Previous Page' width='32' /></a></td>
<td class='online-navigation'><a rel="parent" title="14.3.4 option Callbacks"
  href="optparse-option-callbacks.html"><img src='../icons/up.png'
  border='0' height='32'  alt='Up one Level' width='32' /></a></td>
<td class='online-navigation'><a rel="next" title="14.3.4.7 callback example 4:"
  href="optparse-callback-example-4.html"><img src='../icons/next.png'
  border='0' height='32'  alt='Next Page' width='32' /></a></td>
<td align="center" width="100%">Python Library Reference</td>
<td class='online-navigation'><a rel="contents" title="Table of Contents"
  href="contents.html"><img src='../icons/contents.png'
  border='0' height='32'  alt='Contents' width='32' /></a></td>
<td class='online-navigation'><a href="modindex.html" title="Module Index"><img src='../icons/modules.png'
  border='0' height='32'  alt='Module Index' width='32' /></a></td>
<td class='online-navigation'><a rel="index" title="Index"
  href="genindex.html"><img src='../icons/index.png'
  border='0' height='32'  alt='Index' width='32' /></a></td>
</tr></table>
<div class='online-navigation'>
<b class="navlabel">Previous:</b>
<a class="sectref" rel="prev" href="optparse-callback-example-2.html">14.3.4.5 Callback example 2:</a>
<b class="navlabel">Up:</b>
<a class="sectref" rel="parent" href="optparse-option-callbacks.html">14.3.4 Option Callbacks</a>
<b class="navlabel">Next:</b>
<a class="sectref" rel="next" href="optparse-callback-example-4.html">14.3.4.7 Callback example 4:</a>
</div>
</div>
<hr />
<span class="release-info">Release 2.5.1, documentation updated on 18th April, 2007.</span>
</div>
<!--End of Navigation Panel-->
<address>
See <i><a href="about.html">About this document...</a></i> for information on suggesting changes.
</address>
</body>
</html>
